MC-42652: GraphQL - Expected behavior of add product to cart when SKU already exists

Author: Oleksandr Iegorov

app/code/Magento/QuoteGraphQl/Model/Cart/AddSimpleProductToCart.php

@@ -89,6 +89,12 @@ public function execute(Quote $cart, array $cartItemData): void
         }
 
         try {
+            $items = [];
+            $collection = $cart->getItemsCollection(false);
+            foreach ($collection as $item) {
+                $items[] = $item;
+            }
+            $cart->setItems($items);
             $result = $cart->addProduct($product, $this->buyRequestBuilder->build($cartItemData));
             /*
             $result = $this->addProductToCartWithConcurrency(